Knocker, Ocean View Drive

The very top end of Ocean View Drive may be the heart of the Upper Rockridge neighborhood. Whereas lower Rockridge has little bedrock to speak of, Upper Rockridge is held up by hard Franciscan chert, metabasalt and mélange. The October 1991 fire wiped out this area, and a few lots are still empty. Before the fire, this fine chert knocker graced someone’s back yard. I enjoy having it exposed to the public, but that access has come at a dreadful price.

To get an idea of why I like this knocker so much, see the three closeups labeled “chert” on my free-wallpapers page.

I have no idea. But it’s a name long used by workers in the Franciscan rocks of California. The AGI Glossary cites a 1972 article in the AAPG Bulletin, “What Is Franciscan?” by Berkland et al. The Glossary calls it a handy term for tectonic blocks or exotic blocks. Knockers are the boulders and larger blocks of bedrock you see protruding from the hillsides in the Coast Ranges. They’re the plums in the bedrock pudding called mélange. You won’t see the term used anywhere else in America (possibly in Alaska).